Touch sensor panels are increasingly used as input devices to a computing system. Generally, a touch sensor panel can include a cover substrate (formed from glass, polymer, or the like) to input information via touch and a sensor substrate (also formed from glass, polymer, or the like) with touch sensors to sense the touch on the cover substrate. In a drive to make a thinner touch sensor panel, it is desirable to eliminate the unwanted thickness of the sensor substrate. However, successfully providing a touch sensor panel without the sensor substrate has not been easy.
Elimination of the sensor substrate requires that the touch sensors be located on preferably another existing surface in the panel. One such surface has been the cover substrate. However, the cover substrate has proven to be a difficult option for at least some of the following reasons. In some embodiments, the cover substrate is glass that has been cut and shaped from a motherglass sheet. Then, for strength and durability, the cover glass is typically chemically treated with a strong ionic solution to strengthen all the glass surfaces, including the cut, shaped edges. Because chemical strengthening can damage the thin films of the touch sensors, it can be ineffective to place the touch sensors on the cover glass prior to strengthening. However, after the chemical strengthening has been completed, conventional touch sensor placement processes, such as photolithography and etching, which were developed for the larger motherglass sheets, can be either technically infeasible or too costly for the smaller cover glass. As a result, it can be difficult to use conventional placement processes to place the touch sensors on the cover glass after strengthening.
Accordingly, this approach to thinner touch sensor panels has been problematic.